Diabetes mellitus is a medical condition where the levels of blood glucose are elevated and if left untreated leads to coma and death. The sufferer has great difficulty in controlling their blood glucose level, typically leaving them in a chronic state of hyperglycaemia, or high blood glucose level. There are two major forms of persistent, and currently incurable, diabetes, type 1 and type 2 diabetes. Type 1 diabetics have lost the ability to produce the hormone insulin due to the destruction of the islets of Langerhans in the pancreas. The reason for the destruction is an autoimmune condition but the trigger for this is unknown. Type 1 diabetics must take regular insulin injections, up to 6 per day, to provide their body with enough insulin to allow the cells of their body to process glucose correctly. Insulin administration, along with careful monitoring of diet and exercise, can allow a diabetic to live a relatively normal life. Type 1 diabetes affects around 140,000 Australians and more than 24 million people worldwide. Approximately 4,400 Australian children have type 1 diabetes, with 800 new cases diagnosed per year. Globally, 430,000 children have type 1 diabetes with 65,000 new cases per year. The annual incidence rate of type 1 diabetes in children is growing at about 3% a year. Type 2 diabetes, which is also known as maturity onset diabetes, is due to a premature failure of the islets to produce adequate insulin levels to control the blood glucose values. It affects about 6 to 8% of the population over 50. Both types suffer the same complications from long standing hyperglycaemia.
Chronic hyperglycaemia can cause a number of long term complications, including blindness, chronic renal failure (it is now the most common cause for long term dialysis), ulceration of the lower limbs which may lead to amputation, heart attacks, stroke and neuropathic disease. To reduce the occurrence, onset and severity of these complications, diabetics are advised to keep their blood glucose level in the normal range. Type 1 diabetics do this by the administration of insulin and careful planning and tracking of food intake and exercise. However, this can (and does) give rise to the risk of hypoglycaemia, where the blood glucose level (BGL) drops too low (ie below about 3 or 3.5 mmol/l). Hypoglycaemia has a number of symptoms, including dizziness, irritability, slurring of speech and sweating. Left untreated, hypoglycaemia can lead to fainting, unconsciousness, fitting and, in some cases, death. During a severe hypoglycaemic episode, the sufferer may also sustain some brain injury which, over a number of attacks, can lead to measurable, permanent brain damage. “Dead in bed” scenario accounts for approximately 6% of all deaths of type 1 diabetics below the age of 40; it is thought that nocturnal hypoglycaemia is the cause.
Type 2 diabetics are initially controlled with diet and oral hypoglycaemic agents but after about 10 years, approximately one half of all sufferers will need to administer insulin to control the blood glucose levels and they can also have hypoglycaemia.
Beyond the medical complications, there is the obvious physical danger that hypoglycaemia poses to sufferers. The threat of unconsciousness while driving or even just walking down the street is a part of everyday life for people dealing with hypoglycaemia. Hypoglycaemia is often unpredictable due to poor dietary habits (missing a meal), excessive exercise and erratic absorption of subcutaneous insulin. As a result, due to the risk of a severe hypoglycaemic event that may result from insulin treatment (or oral hypoglycaemics), many diabetics avoid “tight control” of blood glucose levels, making them more susceptible to the long term effects of both hyperglycaemia and hypoglycaemia.
Whilst the effects of prolonged hypoglycaemia can be significant, simple and effective treatment can be provided by the diabetic themselves if detected early enough, simply by consuming a sugar (or glucose) rich food source (eg a few jellybeans) so as to raise their blood glucose levels.
Whilst there are some symptoms discussed above which may alert a diabetic to the onset of hypoglycaemia (or during a hypoglycaemic event), these are not reliable or always detectable (such as when the diabetic is asleep). Further, over time, approximately 17% of type 1 diabetics develop hypoglycaemia unawareness, where they are unable to detect the onset of hypoglycaemia. The level of hypoglycaemia unawareness increases with the length of time that the sufferer has had diabetes.
Early work in this area was performed by Heller et al. (Influence of Sympathetic Nervous System on Hypoglycaemic Warning Symptoms, The Lancet, Aug. 15, 1987, p359-363) who studied the effect of mild insulin-induced hypoglycaemia on symptoms, physiological changes and adrenaline responses in aware diabetics, unaware diabetics and controls. In this study, blood glucose was maintained for 30 minutes at levels of 4.5 mmol/l, 3.2 mmol/l, 2.5 mmol/l and again at 4.5 mmol/l for 30 mins. At each stage, symptom scores, adrenaline levels and physiological parameters including tremor, sweating, heart rate and blood pressure reaction time were measured. Statistically significant changes in all three groups was only observed for reaction time and adrenaline levels when blood glucose dropped to the most extreme level of 2.5 mmol/l. Significant changes in symptom score, tremor, blood pressure and sweat levels were only detected for the controls and aware diabetics when blood glucose dropped to the most extreme level of 2.5 mmol/l. Onset of hypoglycaemia (based on statistically significant change from 4.5 mmol/l to 3.2 mmol/l) was only detected for aware diabetics and controls in relation to adrenaline levels, and by all three groups based on reaction times. This work indicated that onset could not be predicted via tremor.
Due to such difficulties, devices for detecting the onset of, or actual hypoglycaemia, have concentrated on continuous monitoring of blood glucose levels. Such devices are typically expensive and invasive, requiring insertion of a needle under the user's skin to contact either blood or interstitial fluid in order to record blood glucose levels. Some non-invasive devices have been developed which attempt to indirectly detect the onset of hypoglycaemia by measuring a combination of physiological parameters, such as skin temperature, resistance (eg sweat levels), respiration rate, heart rate, restlessness or tremors. However, such devices have been limited to use whilst the patient is asleep due to sensitivity, portability and reliability issues.
Thus, there is a need for an inexpensive and reliable wearable device for detecting and alerting the user of the onset of hypoglycaemia, or at least to provide such persons with a useful alternative.